Field of the Invention
The present invention is directed to remote control systems in which two or more degrees of freedom of the remote device is controlled by remote control, and, in particular, systems in which both angular and translational movement of the remote device is remotely controlled by a remote control.
Description of the Related Art
Motion sensors that provide 3-DOF rotational control have become largely available in the consumer market and can be found in almost all smartphones and other portable computing devices. Their ubiquity is due in large part to modern advances in MEMS technology that allow manufactures to fabricate miniaturized Inertial Measurement Units (IMUs) at a low cost and at a large scale. Besides key advancements in industrial engineering, what makes rotational measurements units convenient to design and produce is that the Earth's gravitational and magnetic fields provide a readily available global fixed coordinate frame for the sensing components to use a reference. As a result, many devices that measure 3-DOF include electromechanical components that respond to gravity's acceleration (e.g., accelerometers) and the direction of Earth's magnetic pole (e.g., magnetometers).
Conversely, devices that can measure full 6-DOF (3 rotational and 3 translational) are substantially more difficult to produce, partly because there is no global reference frame for 3D positions that is easy to exploit. For large-scale measurements of position, one can use triangulation afforded by geostationary satellites in the form of global positioning systems, but the measurements provided by this modality are not reliable for small-scale applications where robustness and accuracy are important. Commercially available solutions that can measure 6-DOF accurately at a small-scale are generally expensive, difficult to set up (complex and large physical footprints), and suffer from several limitations (e.g., cumbersome calibration procedures) that make them impractical for general users. Common examples include multi-camera optical tracking systems (e.g., Polaris® Vicra®) and magnetic systems (e.g., Polhemus™ Patriot).
The problem can be largely simplified by further constraining the degrees of freedom of the sensing unit if doing so makes sense for the application at hand. For instance, knowing that the translational motion of the device is constrained to a flat plane or the surface of a sphere can simplify the computations needed to correlate raw measurements to the physical configuration of the device, and can improve accuracy. Furthermore, the designer may separate the sensing units that measure translation and rotation. This way, not only the complexity of the apparatus decreases, but it allows reusing commercially available devices at consumer prices that already measure each component separately without the need of designing and manufacturing custom hardware. The invention presented in this document hinges on the latter. Furthermore, while users can use gravity (the down vector) as a clear guidance to orient a sensing device that provides three rotational or angular DOFs to control a nearby remote system, a clear physical reference does not exist for translational motion. By using a tablet endowed with a display as a surface for translation, we can display a clear visual reference to the user to guide the motion.
The emergence of affordable, easy-to-use ultrasound simulators has spearheaded the development of novel low-cost motion tracking solutions. The challenge is to create sensors capable of measuring position and orientation as well as physical compression accurately and with minimal encumbrance for the user. Existing motion-tracking technologies and disclosed inventions used for tracking ultrasound probes for medical education and training (simulation) purposes are limited by the lack of realistic and affordable simulated compression. The inability to access reliable, portable, and affordable simulated ultrasound probe movement coupled with compression of tissues with resultant conversion of the compression forces into proportionate ultrasound data (image) deformation is a limitation to ultrasound simulation and training. This described invention introduces an effective solution that addresses multiple sensing requirements (i.e., motion tracking and compression) of ultrasound simulators. In one embodiment, the proposed solution consists of a single array of pressure sensors capable of measuring the contact mechanics of a probe or other relevant apparatus that is placed directly on its surface. From successive measurements of pressure distribution, a proposed tracking algorithm can extrapolate the exact position of the device as well as the amount of mechanical force exerted on the surface. This information is then coupled with ultrasound data with resultant proportionate tissue deformation. This approach overcomes a significant barrier to accurate and robust ultrasound simulation. In another embodiment we introduce the use of more traditional capacitive or resistive surfaces for tracking the position of a probe or other relevant apparatus.
Ultrasound simulators aim at reproducing the experience of using a real ultrasound transducer on a real patient as faithfully as possible. To achieve this goal, most commercially available products provide the user with a handheld device (scanning probe) that can sense its orientation and/or position in 3D space. The orientation and position of the scanning probe is then transmitted to a computer system that simulates how an ultrasound beam interacts with anatomy in the virtual environment and generates an appropriate ultrasound image on screen. In order to increase realism, the scanning probe is often designed to emulate the shape and weight of a real ultrasound transducer.
Many commercially available systems rely on 6 degree-of-freedom (DOF) magnetic, optical, or mechanical trackers. These tracking technologies are expensive, require a laborious set up, and suffer from several limitations. Magnetic trackers are highly susceptible to ferromagnetic interference and thus behave poorly in typical environments where the simulation station is surrounded by a variety of ferrous objects. Optical trackers are very accurate but require the user to maintain a clear line of sight between the handheld device and the tracking system, which is a major limitation in terms of usability. Mechanical trackers are bulky and unsuitable for many applications that require light and portable solutions. Furthermore, in most cases, the user needs to carefully install at least one component of the system externally to act as a reference adding to the system's complexity and encumbrance.
More recent simulators have achieved an adequate level of realism by restricting the sensing solution to 3DOF orientation and traded off the lack of position sensing with some other mechanism for identifying anatomical landmarks on the body. The success of these solutions is that they encapsulate the entirety of the motion sensing technology in the handheld scanning probe using modern MEMS ICs.
An alternative and very effective compromise is the pursuit of 5DOF solutions that restrict tracking of position to a 2D surface (not necessarily planar) and measure orientation in 3D. 5DOF tracking allows the system to measure the position of the handheld device as it slides over the profile of a body and registers its 3D orientation at each point. The advantage of this approach is that, with one fewer spatial dimension to track and a more constrained motion path, it enables engineers to build practical, accurate and self-contained solutions at lower cost compared to traditional solutions for full 6DOF tracking. Various authors have proposed 2D surface tracking solutions based on optical navigation sensors (used in computer mice) and optical tracking of non-repeating dot patterns. While acceptable, these optical solutions have several shortcomings: (1) They may not work well if the lens assembly of the optical sensor is not parallel to surface it tracks; and (2) the optics does not easily fit in objects whose contact surface is very small (e.g. the tip of a needle).
Hence, currently available and proposed simulated ultrasound probes do not have the required elements to accurately reproduce the movements and motions associated with real-life ultrasound guided procedures. This limits the ability to have simulation serve as a training and proficiency assessment tool.
In addition, in the context of ultrasound simulation, it is desirable to augment motion sensing with the ability to measure the mechanical pressure exerted by the scanning probe over a surface. In a real clinical setting, compressing the body of a patient by applying force with the ultrasound transducer during a scan causes the underlying soft tissue to deform, and ultrasound technicians use this phenomenon to differentiate various types of anatomical structures based on their elastic properties as observed in the ultrasound image.